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Center and/or Scale Data

center_scale.Rd

A function to center and/or scale a data matrix.

Usage

center_scale(data, par_tbl = NULL, feat = NULL, center = TRUE, scale = TRUE)

is_center_scaled(data)

undo_center_scale(data, feat = NULL)

Arguments

data

A tibble, data.frame, or matrix object with named data variables to center and/or scale. If matrix, should only contain numeric data.

par_tbl

A tibble containing the mean and standard deviations to use in processing the data. Must also contain an feature column to synchronize the features with their corresponding scaling parameters. If NULL, a parameter table is generated based on data, i.e. data is its own reference.

feat

character(n). A vector indicating which variables to center/scale.

center

logical(1). Whether the variables should be shifted to be zero centered (\(\mu = 0\)).

scale

logical(1). Whether the variables should be scaled to have unit variance (\(\sigma = 1\)).

Value

A center/scaled object of the same class as data. Only features specified in feat are modified.

Functions

  • is_center_scaled(): tests for presence of par_tbl entry in attributes and if it contains appropriate parameter information that can be used for centering or scaling data.

  • undo_center_scale(): the inverse of center_scale(). Undo the transformation.

Author

Stu Field

Examples

scaled <- center_scale(mtcars)
apply(feature_matrix(scaled), 2, mean) |> sum()  # mean ~ 0
#> [1] -1.653191e-15
apply(feature_matrix(scaled), 2, sd)             # sd ~ 1
#>  mpg  cyl disp   hp drat   wt qsec   vs   am gear carb 
#>    1    1    1    1    1    1    1    1    1    1    1 

idx <- withr::with_seed(1,
  sample(1:nrow(mtcars), size = nrow(mtcars) / 2)
)
train <- mtcars[idx, ]
test  <- mtcars[-idx, ]

# Pass `par_tbl` as reference
ft <- c("disp", "hp", "drat")
par <- tibble::tibble(feature = ft,
                      means   = colMeans(feature_matrix(train, ft)),
                      sds     = apply(feature_matrix(train, ft), 2, sd))
cs <- center_scale(test, par_tbl = par)
# Logical test
is_center_scaled(cs)
#> [1] TRUE
# Example of `undo_center_scale()`; reverse above
old <- undo_center_scale(cs)

# check values are reverted
all.equal(test, old)
#> [1] "Attributes: < Component “class”: Lengths (1, 2) differ (string compare on first 1) >"
#> [2] "Attributes: < Component “class”: 1 string mismatch >"